Solenoid valve

Abstract

The invention relates to a solenoid valve made using certain materials which is capable of operation at high frequencies and which can be made as a compact unit. The plunger ( 1 ) is made from an electromagnetic material having a saturation flux density greater than 1.2 Tesla preferably more than 1.6 Tesla, the bore leading from the valve head chamber ( 14 ) to the nozzle orifice ( 12 ) has a length to diameter ratio of less than 5:1 preferably between 2:1 and 4:1 and the nozzle orifice ( 12 ) has a diameter of 80 micrometer or less. The invention also relates to method for operating a drop on demand ink jet printer incorporating such a valve.

1. A valve mechanism for controlling the flow of fluid therethrough, comprising:
 a plunger member journalled for axial reciprocation between a rest and an operative position within a tubular member supporting an electric coil under the influence of a magnetic field generated by that coil when an electric current passes through the coil; 
 bias means to bias the plunger towards its rest position when no current is applied to the coil, the distal end of the plunger extending into a valve head chamber having an outlet bore to a nozzle orifice, the reciprocation of the plunger being adapted to open or close a fluid flow path from the valve head chamber through that bore to the nozzle orifice; and wherein: 
 a. the plunger is made from an electromagnetic material having a saturation flux density greater than 1.2 Tesla; and 
 b. the bore leading from the valve head chamber to the nozzle orifice has a length to diameter ratio of 5:1 or less; and 
 c. the nozzle orifice has a diameter of 80 micrometers or less. 
 
   
   
     2. A valve as claimed in  claim 1 , wherein the plunger is made from a material having a saturation flux density of more than 1.4 Tesla. 
   
   
     3. A valve as claimed in  claim 2 , wherein the plunger is made from a material having a saturation flux density of more than 1.6 Tesla. 
   
   
     4. A valve as claimed  claim 1 , wherein the plunger is made from a material having a coercivity of less than 0.25 amperes per meter and a permeability in excess of 50,000. 
   
   
     5. A valve as claimed in  claim 1 , wherein in that the bore has a length to diameter ratio from 1.5:1 to 5:1. 
   
   
     6. A valve as claimed in  claim 1 , wherein the bore has a length to diameter ratio of from 2:1 to 4:1. 
   
   
     7. A valve as claimed in  claim 1 , wherein the bore has a diameter of from 40 to 60 micrometers. 
   
   
     8. A valve as claimed in  claim 1 , wherein the plunger has a diameter of 2.5 mms or less and a length of from 5 to 15 mms. 
   
   
     9. A valve as claimed in  claim 1 , wherein the bore has an internal axial bore formed therein. 
   
   
     10. A valve as claimed in  claim 1 , wherein the nozzle orifice is formed in a foil nozzle plate carrying a plurality of valves mounted thereon, each nozzle orifice being in register with the plunger of a valve mechanism. 
   
   
     11. A valve as claimed in  claim 10 , wherein the nozzle bore and the nozzle orifice are formed as a single component with the nozzle plate. 
   
   
     12. A valve as claimed in  claim 1 , wherein the coil is wound or formed directly upon the tubular member within which the plunger is to move. 
   
   
     13. A valve as claimed in  claim 1 , wherein the distal wall of the valve head chamber carries one or more upstanding areas to provide an enhanced seal between the opposed end faces of the plunger and the distal wall. 
   
   
     14. A valve as claimed in  claim 13 , wherein the sealing areas are provided by one or more ribs substantially concentric with the inlet to the nozzle bore. 
   
   
     15. A valve as claimed in  claim 1 , wherein the coil is a single winding upon the tubular support member. 
   
   
     16. A valve as claimed in  claim 1 , wherein a metal container is provided as a magnetic return path to the coil. 
   
   
     17. An array of the valves as claimed in  claim 16 , wherein the metal containers surround individual coils in the array. 
   
   
     18. A valve as claimed in  claim 1 , wherein the plunger and tubular member do not have congruent cross sections whereby axial fluid flow paths are formed between the tubular member and the plunger. 
   
   
     19. A drop on demand ink jet printer, comprising:
 a. a reservoir; 
 b. a nozzle orifice; and 
 c. a valve for regulating the flow of ink from the reservoir to the nozzle orifice, the valve comprising
 1. a plunger member journalled for axial reciprocation between a rest and an operative position within a tubular member supporting an electric coil under the influence of a magnetic field generated by that coil when an electric current passes through the coil; 
 2. bias means to bias the plunger towards its rest position when no current is applied to the coil, the distal end of the plunger extending into a valve head chamber having a outlet bore to a nozzle orifice, the reciprocation of the plunger being adapted to open or close a fluid flow path from the valve head chamber through that bore to the nozzle orifice; and 
 wherein, the plunger is made from an electromagnetic material having a saturation flux density greater than 1.2 Tesla, the bore leading from the valve head chamber to the nozzle orifice has a length to diameter ratio of 5:1 or less, and the nozzle orifice has a diameter of 80 micrometers or less. 
 
 
   
   
     20. A drop on demand ink jet printer as set forth in  claim 19 , wherein the valve is operated at a frequency greater than 1 kHz. 
   
   
     21. A drop on demand printer as claimed in  claim 19 , further comprising a computer adapted to control the operation of the printer, wherein the computer is adapted to operate in combination with a mechanism for observing the printed dot of ink or other fluid applied to a substrate, the computer being programmed to detect differences between the observed dot and the desired dot and to apply a correction to the current applied to the coil of the valve regulating the flow of fluid to a nozzle orifice so as to maintain the desired observed dot parameters. 
   
   
     22. A method for operating a printer as claimed in  claim 21 , wherein the computer is programmed to operate with byte signals. 
   
   
     23. A method for operating a printer as claimed in  claim 21 , wherein the performance of the valve is calibrated using the comparison of the observed and desired parameters for the printed dots so as to provide one or more records of variations to the operation of the valve required to achieve the desired print parameter. 
   
   
     24. A method for operating a printer as claimed in  claim 21 , wherein the computer modifies the operation of the valve so as to decelerate the plunger at its approaches either or both extreme of its travel. 
   
   
     25. A method as claimed in  claim 21  characterized in that the desired parameters are stored in one or more look up tables for comparison with the observed parameters.